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Nutrient Management

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Written by: 
Mary Concklin, UConn

Fertilizer decisions for fruit crops should be made based on scientific evidence of need. This is accomplished by combining results of foliar tissue and soil testing, with environmental conditions and crop load to develop a fertilizer program.

Foliar tissue analysis indicates the levels of macro and micro nutrients within the plant tissue. Standards have been established for tree fruit.

Foliar tissue collection timing: 60 to 70 days after Petal Fall. Collect 70 to 100 of the most recent mature leaves from trees of the same variety. All labs use the sample testing method. Suggest sampling every 1 to 3 years for maintenance.

A soil analysis indicates the levels of macro nutrients (not nitrogen) and some micro nutrients available in the soil, as well as soil pH.

Soil sample collection timing: anytime the soil is not frozen. One sample will cover 10 acres unless there are changes in topography, previous fertility practices across the area have not been uniform, and if crops vary. Sample every 3 to 5 years. There are three different soil  testing methods (Morgan, Modified Morgan and Mehlich 3). All are correct. However, in order to compare a field from one testing to another, use the same soil testing lab each time.

When decisions are made based on previous experience, a grower could be missing interactions of elements that are hindering production and/or quality.  This can also lead to the over or over-application of nutrients. Although recommendations on fertilizer containers have a scientific basis, they are considered a maintenance amount and are not reflective of the nutrient needs of a specific farm site. Plant age does not take into account specific plant needs, or soil nutrient levels. When fertilizer decisions are based on visual appearance, reductions in crop yield or quality may have already occurred. Diagnosing based on appearance alone does not take into account nutrient interactions.

Excessive rates of certain nutrients can cause interactions leading to deficiencies of other nutrients. For example, high rates of nitrogen can lead to an induced potassium deficiency which has a negative impact on winter hardiness and fruit size. An over application of potassium can lead to an induced deficiency of calcium. The lack of scientific evidence when making fertilizer decisions can result in over- as well as under-applications of many nutrients. The resulting imbalance can affect yield, quality, and may contribute to ground or surface water contamination. An excess amount of phosphorus doesn’t impede plant growth but creates environmental problems that are well documented. Nutrient imbalances can also affect the longevity of a planting which can have an economic impact on a farming operation. Nutrient deficiencies can result in stunted growth, reduced fruit yield and quality, and overall reduced plant health. Excessive rates of nutrients can cause a delay in fruit maturity, an over-abundance of vegetative growth, reduced bud set, and an increase in insect and disease problems. Improper soil pH for a crop can lead to nutrient deficiencies and toxicities affecting fruit quality and plant health.

Stone fruit foliar tissue optimum levels
Nutrient optimum foliar levels
Nitrogen (N)

3.0 to 4.2 % (Peach, Nectarine)

2.4 to 3.4 % (All other stone fruit)

Phosphorus (P) 0.08 to 0.33 %
Potassium (K) 1.3 to 1.9 %
Calcium (Ca) 1.3 to 2.0 %
Magnesium (Mg) 0.4 to 0.7 %
Boron (B) 35 to 50 ppm
Iron (Fe) 80 to 500 ppm
Manganese (Mn) 35 to 135 ppm
Copper (Cu) 7 to 12 ppm
Zinc (Zn) 25 to 50 ppm
Stone Fruit Soil test optimum levels
Nutrient Soil test optimum level
pH

6.5 to 7.0 (Pre-plant)

6.0 to 6.5 (Established)

Phosphorus (P)

>10 lb (Pre-plant)

9 lb (Established)

Potassium (K) 240 lb
Calcium (Ca) 2400 lb
Magnesium (Mg) 400 lb